Tuesday 19 July 2011 01.00 EDT
First published on Tuesday 19 July 2011 01.00 EDT

More than the fate of a global media empire rides on the cross-examination of Rupert Murdoch, his son James and "fifth daughter" Rebekah Brooks by the Commons media select committee. Backbench MPs have the chance to demonstrate that this vital forum of scrutiny and accountability has finally come of age after 150 years of trying.

One of the brighter features of the grim phone-hacking saga has been the sight of rank and file MPs in all parties at Westminster asserting themselves against trangressions by the press, the police and by the executive branch of government which so often cowed them throughout the 20th century. "No grandstanding please" and "questions, not speeches", MPs whisper to John Whittingdale, the panel's Tory chairman.

In the new broom mood of the 2010 parliament the willingness of some Conservative and Lib Dem MPs has been a healthy development, more numerically effective in a coalition than in the decades of huge Thatcher-Blair majorities. So has the reformist Speaker John Bercow's willingness to grant many more emergency statements and – last week – a full debate on the Murdoch affair. David Cameron was forced to join Labour condemnation of the BSkyB bid.

Yet, now that the Commons chamber rarely proves a game-changer, select committees have become the crucial platform in the decades since Margaret Thatcher sanctioned their modernisation in 1979.

There had been ad hoc committees to investigate scandal or policy failure for centuries. Then in 1861 the public accounts committee (PAC) was established to check whether public money was being well spent. But mostly the system remained ad hoc until Thatcher allowed formation of a select committee to monitor each department. She clipped their wings by denying them enough resources, the staff and legal advice open to US congressional committees, paid chairmen or the power to compel ministers to attend – or even to make them respond to their reports.

Slowly but surely those constrictions have been overturned. Committees have more prestige; membership is in growing demand. An analysis by UCL's constitution unit in June revealed that 40% of committee recommendations were accepted by ministers and a similar proportion implemented.

More important is their role – as with the Murdochs and the Met police – in airing problems, highlighting failure (the defence select committee this week criticised military mismanagement of the Helmand conflict) and "generating fear" among policymakers that they may be caught out.

In 1992, the same year the two sons of Robert Maxwell hid behind their lawyers in front of a committee, the industry panel produced an influential report on coal. Another tycoon was threatened with the Sergeant at Arms if he didn't turn up.

But there were also painful failures, not least when the foreign affairs committee browbeat Dr David Kelly two days before the weapons expert killed himself in 2003.

Crucially, after the expenses scandal of 2009 several modest reforms agreed by a repentent political class included the creation of a backbench committee to share control of the Commons timetable and the election of select committee chairmen by MPs in secret ballot, not by nods and winks from party whips. The impact has been dramatic.

Traditionally, the governing party (or coalition) has had a majority on each committee but only chairs the most important ones, where government whips always tried to promote trusties and to sack troublemakers such as Gwyneth Dunwoody (transport) or Nick Winterton (health). Elections ensured that Andrew Tyrie, the formidable chair of the Treasury select committee, was in place to give ministers and bankers a sceptical hearing. This year he has started gaining congressional veto power over "A list" nominees to public bodies.

The mild-mannered Stephen Dorrell has proved a formidable cross-party critic of Andrew Lansley's health bill. Richard Ottoway craftily staged a full Commons debate on the foreign affairs committee's critical report of cuts at the BBC World Service – and won concessions. Labour's Keith Vaz is a bit of a grandstander at home affairs where police chiefs were roughed up last week. But Clive Best does well at local government and Margaret Hodge at the PAC which (uniquely) has a staff of 800 of the National Audit Office at its elbow.

John Whittingdale's panel has the chance to consolidate these gains - or knock them back. "Don't mess it up," say colleagues.